1. Field of the Invention
The present invention is broadly concerned with improved prostheses particularly designed for hip arthroplasties in order to securely hold the head of the femur, whether anatomical or prosthetic, thereby reducing the occurrences of dislocation of hip prostheses. More particularly, the invention pertains to a prosthesis for total hip arthroplasty comprising a metal ring constrained acetabular insert having a liner which is fixed to a person's pelvis by a shell to receive the prosthetic femur head in the liner. In preferred forms, the acetabular liner covers greater than 180° of the prosthetic femur head, and the metal ring is substantially rigid surrounding the opening of the liner to inhibit deformation of the liner and dislocation of the hip joint.
2. Description of Prior Art
To repair a hip joint, it is common to attach a shell to a patient's pelvis. A liner is typically received in the shell, and the ball or head of the femur is held in the liner. While the use of these prostheses is well established, the ball of the femur occasionally dislocates from the liner or the liner comes out of the shell. Such dislocations are debilitating and extremely painful. Some types of hip prostheses are more prone to dislocations, so that the patients must undergo additional surgery to replace or repair the prostheses. The dislocations typically occur because the liner is not securely held in the shell the liner does not engage enough of the ball of the femur, and/or the liner is too easily deformed. Thus, the force or torque required to disengage the ball of the femur from the liner, or the liner from the shell, is much less than the force or torque required to disengage the shell from the pelvis thereby permitting the ball of the femur to come out of the liner, or the liner to come out of the shell, too frequently.